This invention relates to testing equipment for bridge type transducers. More particularly, this invention relates to semi-automated testing systems for bridge type transducers and have the capability to test several transducers at once. The word "transducer" is meant to include any full bridge measuring device, e.g., pressure transducers, load cells, accelerometers, etc.
Prior art methods of testing and calibrating bridge type transducers have been done by manual testing of one transducer at a time. The normal calibration procedure for a bridge type transducer is to apply about twenty known load levels onto the transducer and then measure the output voltage of the transducer at each of these known load levels. This then provides a listing of load levels versus the ratio of the output voltage to the input voltage of the transducer. Normally this is expressed not as the curve of the individual points but rather a best fit linear curve specified by a slope and an intercept. Once the calibrated transducer is sent to the field, it then becomes very inconvenient to retest the transducer by the former method. A field check of the transducer may be accomplished by applying a calibration resistor of known resistance in parallel to one of the bridge leg resistors in the transducer. This would also have been done at the time of the lab calibration using the twenty known load levels. The lab testing would then apply the particular calibration resistor of known resistance across a specified leg of the transducer and record a reading which would represent at least 50% of the full scale loading of the transducer. In other words, the calibration resistor simulates a load, although no load is actually applied to the transducer. A field operator would then check the functioning of the transducer by connecting the same known calibration resistance across the same leg to check that the output at that time agreed with the lab recorded calibration resistor output. If the two readings match, this verifies the full range calibration of the bridge type transducer.
Unfortunately, the manual testing process is quite tedious and, therefore, prone to human error. It is common for mistakes to be made in the recording of which leg of the transducer is used for the calibraton resistor test. Another common error is recording the value of the cal resistor used. These problems are aggravated in a testing lab since it is quite common to receive a large number of transducers all at once. There has been an unmet need in the testing industry for an automated system which can produce error free calibration of large numbers of transducers simultaneously.